Unblind equalizer architecture for digital communication systems

ABSTRACT

A method and apparatus for equalizing digital data signals is disclosed. The method comprises the steps of demodulating and decoding an input signal having input data to produce a data output, remodulating the data output to produce a pseudo-training sequence including an idealized input signal, and generating equalizer parameters from the pseudo-training sequence. The apparatus comprises a demodulator for demodulating an input signal to produce a data output, a modulator, communicatively coupled to the demodulator, for remodulating the data output to produce a pseudo-training sequence including an idealized input signal, and a parameter generation module, communicatively coupled to the modulator for generating equalizer parameters from the pseudo-training sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationNo. 60/421,329, entitled “INNOVATIVE UNBLIND EQUALIZER ARCHITECTURE FORDIGITAL COMMUNICATION SYSTEMS,” Weizheng Wang, Tung-Sheng Lin, Ernest C.Chen, and William C. Lindsey, filed Oct. 25, 2002, which application ishereby incorporated by reference herein.

This application is also a continuation-in-part of the following andcommonly assigned patent application(s), all of which applications areincorporated by reference herein:

Application Ser. No. 09/844,401, filed Apr. 27, 2001, now U.S. Pat. No.7,209,524 by Ernest C. Chen, entitled “LAYERED MODULATION FOR DIGITALSIGNALS”.

This application is related to the following applications:

Application Ser. No. 11/653,517, entitled “LAYERED MODULATION FORDIGITAL SIGNALS,” filed on Jan. 16, 2007, by Ernest C. Chen, which is acontinuation of application Ser. No. 09/844,401, entitled “LAYEREDMODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C.Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/165,710, entitled “SATELLITE TWTA ON-LINENON-LINEARITY MEASUREMENT,” filed on Jun. 7, 2002, by Ernest C. Chen,which is a continuation-in-part of application Ser. No. 09/844,401,entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27,2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/236,414, entitled “SIGNAL, INTERFERENCE ANDNOISE POWER MEASUREMENT,” filed on Sep. 6, 2002, by Ernest C. Chen andChinh Tran, which is a continuation-in-part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/693,135, entitled “LAYERED MODULATION FOR ATSCAPPLICATIONS,” filed on Oct. 24, 2003, by Ernest C. Chen, which claimsbenefit to Provisional Patent Application 60/421,327, filed Oct. 25,2002 and which is a continuation-in-part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/913,927, entitled “CARRIER TO NOISE RATIOESTIMATIONS FROM A RECEIVED SIGNAL,” filed on Aug. 5, 2004, by Ernest C.Chen, which is a continuation in part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 11/619,173, entitled “PREPROCESSING SIGNAL LAYERSIN LAYERED MODULATION DIGITAL SIGNAL SYSTEM TO USE LEGACY RECEIVERS,”filed Jan. 2, 2007, which is a continuation of application Ser. No.10/068,039, entitled “PREPROCESSING SIGNAL LAYERS IN LAYERED MODULATIONDIGITAL SIGNAL SYSTEM TO USE LEGACY RECEIVERS,” filed on Feb. 5, 2002,by Ernest C. Chen, Tiffany S. Furuya, Philip R. Hilmes, and JosephSantoru now issued as U.S. Pat. No. 7,245,671, which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/693,421, entitled “FAST ACQUISITION OF TIMINGAND CARRIER FREQUENCY FROM RECEIVED SIGNAL,” flied on Oct. 24, 2003, byErnest C. Chen, now issued as U.S. Pat. No. 7,151,807, which claimspriority to Provisional Patent Application Ser. No. 60/421,292, filedOct. 25, 2002, and which is a continuation-in-part of application Ser.No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filedon Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No.7,209,524;

Application Ser. No. 10/692,491, entitled “ONLINE OUTPUT MULTIPLEXERFILTER MEASUREMENT,” filed on Oct. 24, 2003, by Ernest C. Chen, whichclaims priority to Provisional Patent Application 60/421,290, filed Oct.25, 2002, and which is a continuation-in-part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 11/603,776, entitled “DUAL LAYER SIGNAL PROCESSINGIN A LAYERED MODULATION DIGITAL SIGNAL SYSTEM,” filed on Nov. 22, 2006,by Ernest C. Chen, Tiffany S. Furuya, Philip R. Hilmes, and JosephSantoru, which is a continuation of application Ser. No. 10/068,047,entitled “DUAL LAYER SIGNAL PROCESSING IN A LAYERED MODULATION DIGITALSIGNAL SYSTEM,” filed on Feb. 5, 2002, by Ernest C. Chen, Tiffany S.Furuya, Philip R. Hilmes, and Joseph Santoru, now issued as U.S. Pat.No. 7,173,981, which is a continuation-in-part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/962,346, entitled “COHERENT AVERAGING FORMEASURING TRAVELING WAVE TUBE AMPLIFIER NONLINEARITY,” filed on Oct. 8,2004, by Ernest C. Chen, which claims priority to Provisional PatentApplication Ser. No. 60/510,368, filed Oct. 10, 2003, and which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 11/655,001, entitled “AN OPTIMIZATION TECHNIQUE FORLAYERED MODULATION,” flied on Jan. 18, 2007, by Weizheng W. Wang,Guancai Zhou, Tung-Sheng Lin, Ernest C. Chen, Joseph Santoru, andWilliam Lindsey, which claims priority to Provisional Patent Application60/421,293, filed Oct. 25, 2002, and which is a continuation ofapplication Ser. No. 10/693,140, entitled “OPTIMIZATION TECHNIQUE FORLAYERED MODULATION,” filed on Oct. 24, 2003, by Weizheng W. Wang,Guancai Zhou, Tung-Sheng Lin, Ernest C. Chen, Joseph Santoru, andWilliam Lindsey, now issued as U.S. Pat. No. 7,184,489, which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 11/656,662, entitled “EQUALIZERS FOR LAYEREDMODULATION AND OTHER SIGNALS,” filed on Jan. 22, 2007, by Ernest C.Chen, Tung-Sheng Lin, Weizheng W. Wang, and William C. Lindsey, whichclaims priority to Provisional Patent Application 60/421,241, filed Oct.25, 2002, and which is a continuation of application Ser. No.10/691,133, entitled “EQUALIZERS FOR LAYERED MODULATED AND OTHERSIGNALS;” filed on Oct. 22, 2003, by Ernest C. Chen, Tung-Sheng Lin,Weizheng W. Wang, and William C. Lindsey, now issued as U.S. Pat. No.7,184,473, which is a continuation-in-part of application Ser. No.09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed onApr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/961,579, entitled “EQUALIZATION FOR TWTANONLINEARITY MEASUREMENT” filed on Oct. 8, 2004, by Ernest C. Chen,which is a continuation-in-part of application Ser. No. 09/844,401,entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27,2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/532,632, entitled “LOWER COMPLEXITY LAYEREDMODULATION SIGNAL PROCESSOR,” filed on Apr. 25, 2005, by Ernest C. Chen,Weizheng W. Wang, Tung-Sheng Lin, Guangcai Zhou, and Joseph Santoru,which is a National Stage Application of PCT US03/32264, filed Oct. 10,2003, which claims priority to Provisional Patent Application60/421,331, entitled “LOWER COMPLEXITY LAYERED MODULATION SIGNALPROCESSOR,” filed Oct. 25, 2002, by Ernest C. Chen, Weizheng W. Wang,Tung-Sheng Lin, Guangcai Zhou, and Joseph Santoru, and which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524;

Application Ser. No. 10/532,631, entitled “FEEDER LINK CONFIGURATIONS TOSUPPORT LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 25, 2005,by Paul R. Anderson, Joseph Santoru and Ernest C. Chen, which is aNational Phase Application of PCT US03/33255, filed Oct. 20, 2003, whichclaims priority to Provisional Patent Application 60/421,328, entitled“FEEDER LINK CONFIGURATIONS TO SUPPORT LAYERED MODULATION FOR DIGITALSIGNALS,” flied Oct. 25, 2002, by Paul R. Anderson, Joseph Santoru andErnest C. Chen, and which is a continuation-in-part of application Ser.No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filedon Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No.7,209,524;

Application Ser. No. 10/532,619, entitled “MAXIMIZING POWER AND SPECTRALEFFICIENCIES FOR LAYERED AND CONVENTIONAL MODULATIONS,” filed on Apr.25, 2005, by Ernest C. Chen, which is a National Phase Application ofPCT Application US03/32800, filed Oct. 16, 2003, which claims priorityto Provisional Patent Application 60/421,288, entitled “MAXIMIZING POWERAND SPECTRAL EFFICIENCIES FOR LAYERED AND CONVENTIONAL MODULATION,”filed Oct. 25, 2002, by Ernest C. Chen and which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524,

Application Ser. No. 10/532,524, entitled “AMPLITUDE AND PHASE MATCHINGFOR LAYERED MODULATION RECEPTION,” filed on Apr. 25, 2005, by Ernest C.Chen, Jeng-Hong Chen, Kenneth Shum, and Joungheon Oh, which is aNational Phase Application of PCT Application US03/31199, filed Oct. 3,2003, which claims priority to Provisional Patent Application60/421,332, entitled “AMPLITUDE AND PHASE MATCHING FOR LAYEREDMODULATION RECEPTION,” filed Oct. 25, 2002, by Ernest C. Chen, Jeng-HongChen, Kenneth Shum, and Joungheon Oh, and which is acontinuation-in-part of application Ser. No. 09/844,401, entitled“LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, byErnest C. Chen, now issued as U.S. Pat. No. 7,209,524, and also claimspriority to;

Application Ser. No. 10/532,582, entitled “METHOD AND APPARATUS FORTAILORING CARRIER POWER REQUIREMENTS ACCORDING TO AVAILABILITY INLAYERED MODULATION SYSTEMS,” filed on Apr. 25, 2005, by Ernest C. Chen,Paul R. Anderson and Joseph Santoru, now issued as U.S. Pat. No.7,173,977, which is a National Stage Application of PCT ApplicationUS03/32751, filed Oct. 15, 2003, which claims priority to ProvisionalPatent Application 60/421,333, entitled “METHOD AND APPARATUS FORTAILORING CARRIER POWER REQUIREMENTS ACCORDING TO AVAILABILITY INLAYERED MODULATION SYSTEMS,” filed Oct. 25, 2002, by Ernest C. Chen,Paul R. Anderson and Joseph Santoru, and which is a continuation-in-partof application Ser. No. 09/844,401, entitled “LAYERED MODULATION FORDIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issuedas U.S. Pat. No. 7,209,524;

Application Ser. No. 10/532,509, entitled “ESTIMATING THE OPERATINGPOINT ON A NONLINEAR TRAVELING WAVE TUBE AMPLIFIER,” filed on Apr. 25,2005, by Ernest C. Chen and Sharmik Maitra, now issued as U.S. Pat. No.7,230,480, which is a National Stage Application of PCT ApplicationUS03/33130 filed Oct. 17, 2003, and which claims priority to ProvisionalPatent Application 60/421,289, entitled “ESTIMATING THE OPERATING POINTON A NONLINEAR TRAVELING WAVE TUBE AMPLIFIER,” filed Oct. 25, 2002, byErnest C. Chen and Shamik Maitra, and which is a continuation-in-part ofapplication Ser. No. 09/844,401, entitled “LAYERED MODULATION FORDIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issuedas U.S. Pat. No. 7,209,524;

Application Ser. No. 10/519,322, entitled “IMPROVING HIERARCHICAL 8PSKPERFORMANCE,” filed an Dec. 23, 2004 by Ernest C. Chen and JosephSantoru, which is a National Stage Application of PCT US03/020862 filedJul. 1, 2003, which claims priority to Provisional Patent Application60/392,861, filed Jul. 1, 2002 and Provisional Patent Application60/392,860, filed Jul. 1, 2002, and which is also related to applicationSer. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,”filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No.7,209,524;

Application Ser. No. 10/519,375, entitled “METHOD AND APPARATUS FORLAYERED MODULATION,” filed on Jul. 3, 2003, by Ernest C. Chen and JosephSantoru, which is a National Stage Application of PCT US03/20847, filedJul. 3, 2003, which claims priority to Provisional Patent Application60/393,437 filed Jul. 3, 2002, and which is related to application Ser.No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filedon Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No.7,209,524; and

Application Ser. No. 10/692,539, entitled “ON-LINE PHASE NOISEMEASUREMENT FOR LAYERED MODULATION”, filed Oct. 24, 2003, by Ernest C.Chen, which claims priority from Provisional Patent Application60/421,291, filed Oct. 25, 2002, entitled “ON-LINE PHASE NOISEMEASUREMENT FOR LAYERED MODULATION”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and methods for transmittingdata, and in particular to a system and method for equalizing digitaldata signals.

2. Description of the Related Art

Digital signal communication systems have been used in various fields,including digital TV signal transmission, both terrestrial andsatellite. As the various digital signal communication systems andservices evolve, there is a burgeoning demand for increased datathroughput and added services. However, it is more difficult toimplement improvement in old systems and new services when it isnecessary to replace existing legacy hardware, such as transmitters andreceivers. New systems and services are at an advantage when they canutilize existing legacy hardware. In the realm of wirelesscommunications, this principle is further highlighted by the limitedavailability of electromagnetic spectrum. Thus, it is not possible (orat least not practical) to merely transmit enhanced or additional dataat a new frequency.

The conventional method of increasing spectral capacity is to move to ahigher-order modulation, such as from quadrature phase shift keying(QPSK) to eight phase shift keying (8 PSK) or sixteen quadratureamplitude modulation (16 QAM). Unfortunately, QPSK receivers cannotdemodulate conventional 8 PSK or 16 QAM signals. As a result, legacycustomers with QPSK receivers must upgrade their receivers in order tocontinue to receive any signals transmitted utilizing 8 PSK or 16 QAMmodulation.

It is advantageous for systems and methods of transmitting signals toaccommodate enhanced and increased data throughput without requiringadditional frequency. It is also advantageous for enhanced and increasedthroughput signals for new receivers to be backwards compatible withlegacy receivers. There is further advantage for systems and methodswhich allow transmission signals to be upgraded from a source separatefrom the legacy transmitter.

It has been proposed that a layered modulation signal, transmittingnon-coherently upper as well as lower layer signals, be employed to meetthese needs. Such layered modulation systems allow for higherinformation throughput with backwards compatibility. However, even whenbackward compatibility is not required (such as with an entirely newsystem), layered modulation can still be advantageous because itrequires a TWTA peak power significantly lower than that for aconventional 8 PSK or 16 QAM modulation formats for a given throughput.

Equalizers are widely used in communication systems, and areparticularly useful when there are multipath and/or other distortioneffects in the transmission channel. Equalizers can also be used tocancel “echo” in the system. However, such equalizers typically requireapriori knowledge of the channel impulse response, or knowledge of apre-determined training sequence that is transmitted in the channel.Since the training sequence is known, the channel impulse response canbe determined from the training sequence and appropriately equalized.Blind equalizers, which do not have apriori knowledge of the channelimpulse response or knowledge of the pre-determined training sequence,are known, but such equalizers typically exhibit poor performance.

Accordingly, there is a need for systems and methods for accuratelyequalizing communication channels that does not require aprioriknowledge of the channel impulse response or a training sequence. Thepresent invention meets this need and provides further advantages asdetailed hereafter.

SUMMARY OF THE INVENTION

To address the requirements described above, the present inventiondiscloses a method and apparatus for equalizing digital data signals.The method comprises the steps of demodulating and decoding an inputsignal having input data to produce a data output, remodulating the dataoutput to produce a pseudo-training sequence including an idealizedinput signal, and generating equalizer parameters from thepseudo-training sequence. The apparatus comprises a demodulator fordemodulating an input signal to produce a data output, a modulator,communicatively coupled to the demodulator, for remodulating the dataoutput to produce a pseudo-training sequence including an idealizedinput signal, and a parameter generation module, communicatively coupledto the modulator for generating equalizer parameters from thepseudo-training sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a diagram illustrating an overview of a single satellite videodistribution system;

FIG. 2 is a block diagram showing a typical uplink configuration for asingle satellite transponder;

FIG. 3A is a diagram of a representative data stream;

FIG. 3B is a diagram of a representative data packet;

FIG. 4 is a block diagram showing one embodiment of the modulator;

FIG. 5 is a block diagram of an integrated receiver/decoder;

FIGS. 6A-6C are diagrams illustrating the basic relationship of signallayers in a layered modulation transmission;

FIGS. 7A-7C are diagrams illustrating a signal constellation of a secondtransmission layer over the first transmission layer after first layerdemodulation;

FIG. 8 is a diagram showing a system for transmitting and receivinglayered modulation signals;

FIG. 9 is a block diagram depicting one embodiment of an enhancedreceiver/decoder capable of receiving layered modulation signals;

FIG. 10A is a block diagram of one embodiment of the enhancedtuner/modulator and FEC encoder;

FIG. 10B depicts another embodiment of the enhanced tuner/modulatorwherein layer subtraction is performed on the received layered signal;

FIGS. 11A and 11B depict the relative power levels of exampleembodiments of the present invention;

FIGS. 12A and 12B are diagrams illustrating the application of unblindequalization techniques;

FIG. 13 presents an exemplary implementation of an unblind equalizersystem;

FIG. 14 is a diagram illustrating the embodiment shown in FIG. 13, as itcan be applied to a layered modulation system such as are illustrated inFIGS. 10A and 10B;

FIGS. 15A and 15B are diagrams depicting further detail regarding thegeneration of a pseudo-training sequence.

FIG. 16 is a block diagram illustrating an unblind equalizer thatrecursively updates equalizer parameters;

FIG. 17 is a block diagram illustrating the unblind equalizer of FIG. 16as applied to a layered modulation system;

FIGS. 18A and 18B are state transition diagrams depicting alternativeembodiments of the present invention; and

FIG. 19 illustrates an exemplary computer system that could be used toimplement selected modules or functions of the present invention;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which is shown, by way ofillustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which show, by way ofillustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

Video Distribution System

FIG. 1 is a diagram illustrating an overview of a single satellite videodistribution system 100. The video distribution system 100 comprises acontrol center 102 in communication with an uplink center 104 via aground or other link 114 and with a subscriber receiver station 110 viaa public switched telephone network (PSTN) or other link 120. Thecontrol center 102 provides program material (e.g. video programs, audioprograms and other data) to the uplink center 104 and coordinates withthe subscriber receiver stations 110 to offer, for example, pay-per-view(PPV) program services, including billing and associated decryption ofvideo programs.

The uplink center 104 receives program material and program controlinformation from the control center 102, and using an uplink antenna 106and transmitter 105, transmits the program material and program controlinformation to the satellite 108. The satellite receives and processesthis information and transmits the video programs and controlinformation to the subscriber receiver station 110 via downlink 118using transmitter 107. The subscriber receiving station 110 receivesthis information using the outdoor unit (ODU) 112, which includes asubscriber antenna and a low noise block converter (LNB).

In one embodiment, the subscriber receiving station antenna is an18-inch slightly oval-shaped Ku-band antenna. The slight ovoid shape isdue to the 22.5 degree offset feed of the LNB (low noise blockconverter) which is used to receive signals reflected from thesubscriber antenna. The offset feed positions the LNB out of the way soit does not block any surface area of the antenna minimizing attenuationof the incoming microwave signal.

The video distribution system 100 can comprise a plurality of satellites108 in order to provide wider terrestrial coverage, to provideadditional channels, or to provide additional bandwidth per channel. Inone embodiment of the invention, each satellite comprises 16transponders to receive and transmit program material and other controldata from the uplink center 104 and provide such material to thesubscriber receiving stations 110. Using data compression andmultiplexing techniques with respect to channel capabilities, twosatellites 108 working together can receive and broadcast over 150conventional (non-HDTV) audio and video channels via 32 transponders.

While the invention disclosed herein will be described with reference toa satellite-based video distribution system 100, the present inventionmay also be utilized with terrestrial-based transmission of programinformation, whether by broadcasting means, cable, or other means.Further, the different functions collectively allocated among thecontrol center 102 and the uplink center 104 as described above can bereallocated as desired without departing from the intended scope of thepresent invention.

Although the foregoing has been described with respect to an embodimentin which the program material delivered to the subscriber 122 is video(and audio) program material such as a movie, the foregoing method canbe used to deliver program material comprising purely audio informationor other data.

Uplink Configuration

FIG. 2 is a block diagram showing a typical uplink configuration for asingle satellite 108 transponder, showing how video program material isuplinked to the satellite 108 by the control center 102 and the uplinkcenter 104. FIG. 2 shows three video channels (which could be augmentedrespectively with one or more audio channels for high fidelity music,soundtrack information, or a secondary audio program for transmittingforeign languages), a data channel from a program guide subsystem 206and computer data information from a computer data source 208.

The video channels are provided by a program source of video material200A-200C [collectively referred to hereinafter as video source(s) 200].The data from each video program source 200 is provided to an encoder202A-202C [collectively referred to hereinafter as encoder(s) 202]. Eachof the encoders accepts a program time stamp (PTS) from the controller216. The PTS is a wrap-around binary time stamp that is used to assurethat the video information is properly synchronized with the audioinformation after encoding and decoding. A PTS time stamp is sent witheach I-frame of the MPEG encoded data.

In one embodiment of the present invention, each encoder 202 is a secondgeneration Motion Picture Experts Group (MPEG-2) encoder, but otherdecoders implementing other coding techniques can be used as well. Thedata channel can be subjected to a similar compression scheme by anencoder (not shown), but such compression is usually either unnecessary,or performed by computer programs in the computer data source (forexample, photographic data is typically compressed into *.TIF files or*.JPG files before transmission). After encoding by the encoders 202,the signals are converted into data packets by a packetizer 204A-204F[collectively referred to hereinafter as packetizer(s) 204] associatedwith each source 200.

The data packets are assembled using a reference from the system clock214 (SCR) and from the conditional access manager 210, which providesthe SCID to the packetizers 204 for use in generating the data packets.These data packets are then multiplexed into Ser. data and transmitted.

Broadcast Data Stream Format and Protocol

FIG. 3A is a diagram of a representative data stream. The first packetsegment 302 comprises information from video channel 1 (data comingfrom, for example, the first video program source 200A). The next packetsegment 304 comprises computer data information that was obtained, forexample from the computer data source 208. The next packet segment 306comprises information from video channel 5 (from one of the videoprogram sources 200). The next packet segment 308 comprises programguide information such as the information provided by the program guidesubsystem 206. As shown in FIG. 3A, null packets 310 created by the nullpacket module 310 may be inserted into the data stream as desired.

The data stream therefore comprises a series of packets from any one ofthe data sources in an order determined by the controller 216. The datastream is encrypted by the encryption module 218, modulated by themodulator 220 (typically using a QPSK modulation scheme), and providedto the transmitter 222, which broadcasts the modulated data stream on afrequency bandwidth to the satellite via the antenna 106. The receiver500 receives these signals, and using the SCID, reassembles the packetsto regenerate the program material for each of the channels.

FIG. 3B is a diagram of a data packet. Each data packet (e.g. 302-316)is 147 bytes long, and comprises a number of packet segments. The firstpacket segment 320 comprises two bytes of information containing theSCID and flags. The SCID is a unique 12-bit number that uniquelyidentifies the data packet's data channel. The flags include 4 bits thatare used to control other features. The second packet segment 322 ismade up of a 4-bit packet type indicator and a 4-bit continuity counter.The packet type identifies the packet as one of the four data types(video, audio, data, or null). When combined with the SCID, the packettype determines how the data packet will be used. The continuity counterincrements once for each packet type and SCID. The next packet segment324 comprises 127 bytes of payload data, which in the cases of packets302 or 306 is a portion of the video program provided by the videoprogram source 200. The final packet segment 326 is data required toperform forward error correction.

FIG. 4 is a block diagram showing one embodiment of the modulator 220.The modulator 220 optionally comprises a forward error correction (FEC)encoder 404 which accepts the first signal symbols 402 and addsredundant information that are used to reduce transmission errors. Thecoded symbols 405 are modulated by modulator 406 according to a firstcarrier 408 to produce an upper layer modulated signal 410. Secondsymbols 420 are likewise provided to an optional second FEC encoder 422to produce coded second symbols 424. The coded second symbols 424 areprovided to a second modulator 414, which modulates the coded secondsignals according to a second carrier 416 to produce a lower layermodulated signal 418. The resulting signals are then transmitted by oneor more transmitters 420, 422. The upper layer modulated signal 410 andthe lower layer modulated signal 418 are therefore uncorrelated, and thefrequency range used to transmit each layer can substantially orcompletely overlap the frequency spectrum used to transmit the other.The upper layer signal 410, however, must be a sufficiently greateramplitude signal than the lower layer signal 418, in order to maintainthe signal constellations shown in FIG. 6 and FIG. 7. The modulator 220may also employ pulse shaping techniques (illustrated by pulse p(t) 430)to account for the limited channel bandwidth. Although FIG. 4illustrates the same pulse shaping p(t) 430 being applied to bothlayers, different pulse shaping can be applied to each layer as well.

Integrated Receiver/Decoder

FIG. 5 is a block diagram of an integrated receiver/decoder (IRD) 500(also hereinafter alternatively referred to as receiver 500). Thereceiver 500 comprises a tuner/demodulator 504 communicatively coupledto an ODU 112 having one or more LNBs 502. The LNB 502 converts the12.2- to 12.7 GHz downlink 118 signal from the satellites 108 to, e.g.,a 950-1450 MHz signal required by the IRD's 500 tuner/demodulator 504.The LNB 502 may provide either a dual or a single output. Thesingle-output LNB 502 has only one RF connector, while the dual outputLNB 502 has two RF output connectors and can be used to feed a secondtuner 504, a second receiver 500, or some other form of distributionsystem.

The tuner/demodulator 504 isolates a single, digitally modulated 24 MHztransponder and converts the modulated data to a digital data stream.Further details regarding the demodulation of the received signalfollow.

The digital data stream is then supplied to a forward error correction(FEC) decoder 506. This allows the IRD 500 to reassemble the datatransmitted by the uplink center 104 (which applied the forward errorcorrection to the desired signal before transmission to the subscriberreceiving station 110) verifying that the correct data signal wasreceived, and correcting errors, if any. The error-corrected data may befed from the FEC decoder module 506 to the transport module 508 via an8-bit parallel interface.

The transport module 508 performs many of the data processing functionsperformed by the IRD 500. The transport module 508 processes datareceived from the FEC decoder module 506 and provides the processed datato the video MPEG decoder 514 and the audio MPEG decoder 517. In oneembodiment of the present invention, the transport module, video MPEGdecoder and audio MPEG decoder are all implemented on integratedcircuits. This design promotes both space and power efficiency, andincreases the security of the functions performed within the transportmodule 508. The transport module 508 also provides a passage forcommunications between the microcontroller 510 and the video and audioMPEG decoders 514, 517. As set forth more fully hereinafter, thetransport module also works with the conditional access module (CAM) 512to determine whether the subscriber receiving station 110 is permittedto access certain program material. Data from the transport module canalso be supplied to the external communication module 526.

The CAM 512 functions in association with other elements to decode anencrypted signal from the transport module 508. The CAM 512 may also beused for tracking and billing these services. In one embodiment of thepresent invention, the CAM 512 functions as a smart card, havingcontacts cooperatively interacting with contacts in the IRD 500 to passinformation. In order to implement the processing performed in the CAM512, the IRD 500, and specifically the transport module 508 provides aclock signal to the CAM 512.

Video data is processed by the MPEG video decoder 514. Using the videorandom access memory (RAM) 536, the MPEG video decoder 514 decodes thecompressed video data and sends it to an encoder or video processor 516,which converts the digital video information received from the videoMPEG module 514 into an output signal usable by a display or otheroutput device. By way of example, processor 516 may comprise a NationalTV Standards Committee (NTSC) or Advanced Television Systems Committee(ATSC) encoder. In one embodiment of the invention both S-Video andordinary video (NTSC or ATSC) signals are provided. Other outputs mayalso be utilized and are advantageous if high definition programming isprocessed.

Audio data is likewise decoded by the MPEG audio decoder 517. Thedecoded audio data may then be sent to a digital-to-analog (D/A)converter 518. In one embodiment of the present invention, the D/Aconverter 518 is a dual D/A converter, one for the right and leftchannels. If desired, additional channels can be added for use insurround sound processing or secondary audio programs (SAPs). In oneembodiment of the invention, the dual D/A converter 518 itself separatesthe left and right channel information, as well as any additionalchannel information. Other audio formats may be similarly supported, forexample, multi-channel DOLBY DIGITAL AC-3.

A description of the processes performed in the encoding and decoding ofvideo streams, particularly with respect to MPEG and JPEGencoding/decoding, can be found in Chapter 8 of “Digital TelevisionFundamentals,” by Michael Robin and Michel Poulin, McGraw-Hill, 1998,which is hereby incorporated by reference herein.

The microcontroller 510 receives and processes command signals from theremote control 524, an IRD 500 keyboard interface, and/or another inputdevice. The microcontroller receives commands for performing itsoperations from a processor programming memory, which permanently storessuch instructions for performing such commands. The processorprogramming memory may comprise a read-only memory (ROM) 538, anelectrically erasable programmable read-only memory (EEPROM) 522, orsimilar memory device. The microcontroller 510 also controls the otherdigital devices of the IRD 500 via address and data lines (denoted “A”and “D” respectively, in FIG. 5).

The modem 540 connects to the customer's phone line via the PSTN port120. It calls, e.g. the program provider, and transmits the customer'spurchase information for billing purposes, and/or other information. Themodem 540 is controlled by the microprocessor 510. The modem 540 canoutput data to other I/O port types including standard parallel and Ser.computer I/O ports.

The present invention also comprises a local storage unit such as thevideo storage device 532 for storing video and/or audio data obtainedfrom the transport module 508. Video storage device 532 can be a harddisk drive, a read/writable compact disc or DVD, a solid state RAM, orany other storage medium. In one embodiment of the present invention,the video storage device 532 is a hard disk drive with specializedparallel read/write capability so that data may be read from the videostorage device 532 and written to the device 532 at the same time. Toaccomplish this feat, additional buffer memory accessible by the videostorage 532 or its controller may be used. Optionally, a video storageprocessor 530 can be used to manage the storage and retrieval of thevideo data from the video storage device 532. The video storageprocessor 530 may also comprise memory for buffering data passing intoand out of the video storage device 532. Alternatively or in combinationwith the foregoing, a plurality of video storage devices 532 can beused. Also alternatively or in combination with the foregoing, themicrocontroller 510 can also perform the operations required to storeand/or retrieve video and other data in the video storage device 532.

The video processing module 516 input can be directly supplied as avideo output to a viewing device such as a video or computer monitor. Inaddition, the video and/or audio outputs can be supplied to an RFmodulator 534 to produce an RF output and/or 8 vestigial side band (VSB)suitable as an input signal to a conventional television tuner. Thisallows the receiver 500 to operate with televisions without a videooutput.

Each of the satellites 108 comprises a transponder, which acceptsprogram information from the uplink center 104, and relays thisinformation to the subscriber receiving station 110. Known multiplexingtechniques are used so that multiple channels can be provided to theuser. These multiplexing techniques include, by way of example, variousstatistical or other time domain multiplexing techniques andpolarization multiplexing. In one embodiment of the invention, a singletransponder operating at a single frequency band carries a plurality ofchannels identified by respective service channel identification (SCID).

Preferably, the IRD 500 also receives and stores a program guide in amemory available to the microcontroller 510. Typically, the programguide is received in one or more data packets in the data stream fromthe satellite 108. The program guide can be accessed and searched by theexecution of suitable operation steps implemented by the microcontroller510 and stored in the processor ROM 538. The program guide may includedata to map viewer channel numbers to satellite transponders and servicechannel identifications (SCIDs), and also provide TV program listinginformation to the subscriber 122 identifying program events.

The functionality implemented in the IRD 500 depicted in FIG. 5 can beimplemented by one or more hardware modules, one or more softwaremodules defining instructions performed by a processor, or a combinationof both.

The present invention provides for the modulation of signals atdifferent power levels and advantageously for the signals to benon-coherent from each layer. In addition, independent modulation andcoding of the signals may be performed. Backwards compatibility withlegacy receivers, such as a quadrature phase shift keying (QPSK)receiver is enabled and new services are provided to new receivers. Atypical new receiver of the present invention uses two demodulators andone remodulator as will be described in detail hereafter.

In a typical backwards-compatible embodiment of the present invention,the legacy QPSK signal is boosted in power to a higher transmission (andreception) level. This creates a power “room” in which a new lower layersignal may operate. The legacy receiver will not be able to distinguishthe new lower layer signal, from additive white Gaussian noise, and,thus, operates in the usual manner. The optimum selection of the layerpower levels is based on accommodating the legacy equipment, as well asthe desired new throughput and services.

The new lower layer signal is provided with a sufficient carrier tothermal noise ratio to function properly. The new lower layer signal andthe boosted legacy signal are non-coherent with respect to each other.Therefore, the new lower layer signal can be implemented from adifferent TWTA and even from a different satellite. The new lower layersignal format is also independent of the legacy format, e.g., it may beQPSK or 8 PSK, using the conventional concatenated FEC code or using anew Turbo code. The lower layer signal may even be an analog signal.

The combined layered signal is demodulated and decoded by firstdemodulating the upper layer to remove the upper carrier. The stabilizedlayered signal may then have the upper layer FEC decoded and the outputupper layer symbols communicated to the upper layer transport. The upperlayer symbols are also employed in a remodulator to generate anidealized upper layer signal. The idealized upper layer signal is thensubtracted from the stable layered signal to reveal the lower layersignal. The lower layer signal is then demodulated and FEC decoded andcommunicated to the lower layer transport.

Signals, systems and methods using the present invention may be used tosupplement a pre-existing transmission compatible with legacy receivinghardware in a backwards-compatible application or as part of apreplanned layered modulation architecture providing one or moreadditional layers at a present or at a later date.

Layered Signals

FIGS. 6A-6C illustrate the basic relationship of signal layers in alayered modulation transmission. FIG. 6A illustrates a first layersignal constellation 600 of a transmission signal showing the signalpoints or symbols 602. FIG. 6B illustrates the second layer signalconstellation of symbols 604 over the first layer signal constellation600 where the layers are coherent. FIG. 6C illustrates a second signallayer 606 of a second transmission layer over the first layerconstellation where the layers may be non-coherent. The second layer 606rotates about the first layer constellation 602 due to the relativemodulating frequencies of the two layers in a non-coherent transmission.Both the first and second layers rotate about the origin due to thefirst layer modulation frequency as described by path 608.

FIGS. 7A-7C are diagrams illustrating a signal constellation of a secondtransmission layer over the first transmission layer after first layerdemodulation. FIG. 7A shows the constellation 700 before the firstcarrier recovery loop (CRL) and FIG. 7B shows the constellation 704after CRL. In this case, the signal points of the second layer areactually rings 702. FIG. 7C depicts a phase distribution of the receivedsignal with respect to nodes 602.

Relative modulating frequencies cause the second layer constellation torotate around the nodes of the first layer constellation. After thesecond layer CRL, this rotation is eliminated. The radius of the secondlayer constellation is determined by its power level. The thickness ofthe rings 702 is determined by the carrier to noise ratio (CNR) of thesecond layer. As the two layers are non-coherent, the second layer mayalso be used to transmit analog or digital signals.

FIG. 8 is a diagram showing a system for transmitting and receivinglayered modulation signals. Separate transmitters 107A, 107B, as may belocated on any suitable platform, such as satellites 108A, 108B, areused to non-coherently transmit different layers of a signal of thepresent invention. Uplink signals are typically transmitted to eachsatellite 108A, 108B from one or more transmitters 105 via an antenna106. The layered signals 808A, 808B (downlink signals) are received atreceiver antennas 112A, 112B, such as satellite dishes, each with a lownoise block (LNB) 812A, 812B where they are then coupled to integratedreceiver/decoders (IRDs) 500, 802. Because the signal layers may betransmitted non-coherently, separate transmission layers may be added atany time using different satellites 108A, 108B or other suitableplatforms, such as ground based or high altitude platforms. Thus, anycomposite signal, including new additional signal layers will bebackwards compatible with legacy receivers 500, which will disregard thenew signal layers. To ensure that the signals do not interfere, thecombined signal and noise level for the lower layer must be at or belowthe allowed noise floor for the upper layer.

Layered modulation applications include backwards compatible andnon-backwards compatible applications. “Backwards compatible” in thissense describes systems in which legacy receivers 500 are not renderedobsolete by the additional signal layer(s). Instead, even if the legacyreceivers 500 are incapable of decoding the additional signal layer(s),they are capable of receiving the layered modulated signal and decodingthe original signal layer. In these applications, the pre-existingsystem architecture is accommodated by the architecture of theadditional signal layers. “Non-backwards compatible” describes a systemarchitecture which makes use of layered modulation, but the modulationscheme employed is such that pre-existing equipment is incapable ofreceiving and decoding the information on additional signal layer(s).

The pre-existing legacy IRDs 500 decode and make use of data only fromthe layer (or layers) they were designed to receive, unaffected by theadditional layers. However, as will be described hereafter, the legacysignals may be modified to optimally implement the new layers. Thepresent invention may be applied to existing direct satellite serviceswhich are broadcast to individual users in order to enable additionalfeatures and services with new receivers without adversely affectinglegacy receivers and without requiring additional signal frequency.

Demodulator and Decoder

FIG. 9 is a block diagram depicting one embodiment of an enhanced IRD802 capable of receiving layered modulation signals. The enhanced IRD802 includes a feedback path 902 in which the FEC decoded symbols arefed back to a enhanced modified tuner/demodulator 904 and transportmodule 908.

FIG. 10A is a block diagram of one embodiment of the enhancedtuner/modulator 904 and FEC encoder 506. FIG. 10A depicts receptionwhere layer subtraction is performed on a signal where the upper carrierhas been demodulated. The upper layer of the received combined signal1016 from the LNB 502, which may contain legacy modulation format, isprovided to and processed by an upper layer demodulator 1004 to producethe stable demodulated signal 1020. The demodulated signal 1020 is fedto a communicatively coupled FEC decoder 1002 which decodes the upperlayer to produce the upper layer symbols which are output to an upperlayer transport. The upper layer symbols are also used to generate anidealized upper layer signal. The upper layer symbols may be producedfrom the decoder 1002 after Viterbi decode (BER<10⁻³ or so) or afterReed-Solomon (RS) decode (BER<10⁻⁹ or so), in typical decodingoperations known to those skilled in the art. The upper layer symbolsare provided via feedback path 902 from the upper layer decoder 1002 toa re-encoder/remodulator 1006 which effectively produces an idealizedupper layer signal. The idealized upper level signal is subtracted fromthe demodulated upper layer signal 1020.

In order for the subtraction to leave a clean small lower layer signal,the upper layer signal must be precisely reproduced. The modulatedsignal may have been distorted, for example, by traveling wave tubeamplifier (TWTA) non-linearity or other non-linear or linear distortionsin the transmission channel. The distortion effects are estimated fromthe received signal after the fact or from TWTA characteristics whichmay be downloaded into the IRD in AM-AM and/or AM-PM maps 1014, used toeliminate the distortion.

A subtractor 1012 then subtracts the idealized upper layer signal fromthe stable demodulated signal 1020. This leaves the lower-power secondlayer signal. The subtractor 1012 may include a buffer or delay functionto retain the stable demodulated signal 1020 while the idealized upperlayer signal is being constructed. The second layer signal isdemodulated by the lower level demodulator 1010 and FEC decoded bydecoder 1008 according to its signal format to produce the lower layersymbols, which are provided to the transport module 508.

FIG. 10B depicts another embodiment wherein layer subtraction isperformed on the received layered signal. In this case, the upper layerdemodulator 1004 produces the upper carrier signal 1022 (as well as thestable demodulated signal output 1020). An upper carrier signal 1022 isprovided to the remodulator 1006. The remodulator 1006 provides theremodulated signal to the non-linear distortion mapper 1018 whicheffectively produces an idealized upper layer signal. Unlike theembodiment shown in FIG. 10A, in this embodiment, the idealized upperlayer signal includes the upper layer carrier for subtraction from thereceived combined signal 416.

Other equivalent methods of layer subtraction will occur to thoseskilled in the art and the present invention should not be limited tothe examples provided here. Furthermore, those skilled in the art willunderstand that the present invention is not limited to two layers;additional layers may be included. Idealized upper layers are producedthrough remodulation from their respective layer symbols and subtracted.Subtraction may be performed on either the received combined signal or ademodulated signal. Finally, it is not necessary for all signal layersto be digital transmissions; the lowest layer may be an analogtransmission.

The following analysis describes the exemplary two layer demodulationand decoding. It will be apparent to those skilled in the art thatadditional layers may be demodulated and decoded in a similar manner.The incoming combined signal is represented as:

${s_{UL}(t)} = {{f_{U}\left( {M_{U}\mspace{14mu}{\exp\left( {{j\;\omega_{U}t} + \theta_{U}} \right)}{\sum\limits_{m = {- \infty}}^{\infty}{S_{Um}{p\left( {t - {mT}} \right)}}}} \right)} + {f_{L}\left( {M_{L}\mspace{14mu}{\exp\left( {{j\;\omega_{L}t} + \theta_{L}} \right)}{\sum\limits_{m = {- \infty}}^{\infty}{S_{Lm}{p\left( {t - {mT} + {\Delta\; T_{m}}} \right)}}}} \right)} + {n(t)}}$where, M_(U) is the magnitude of the upper layer QPSK signal and M_(L)is the magnitude of the lower layer QPSK signal and M_(L)<<M_(U). Thesignal frequencies and phase for the upper and lower layer signals arerespectively ω_(U), θ_(U) and ω_(U), θ_(U), respectively. The symboltiming misalignment between the upper and lower layers is ΔT_(m). Theexpression p(t−mT) represents the time shifted version of the pulseshaping filter p(t) 430 employed in signal modulation. QPSK symbolsS_(Um) and S_(Lm) are elements of

$\left\{ {{\exp\left( {j\frac{n\;\pi}{2}} \right)},{n = 0},1,2,3} \right\}.$f_(U)(·) and f_(L)(·) denote the distortion function of the TWTAs forthe respective signals.

Ignoring f_(U)(·) and f_(L)(·) and noise n(t), the following representsthe output of the demodulator 1004 to the FEC decoder 1002 afterremoving the upper carrier:

${s_{UL}^{\prime}(t)} = {{M_{U}{\sum\limits_{m = {- \infty}}^{\infty}{S_{Um}{p\left( {t - {mT}} \right)}}}} + {M_{L}\exp\left\{ {{{j\left( {\omega_{L} - \omega_{U}} \right)}t} + \theta_{L} - \theta_{U}} \right\}{\sum\limits_{m = {- \infty}}^{\infty}{S_{Lm}{p\left( {t - {mT} + {\Delta\; T_{m}}} \right)}}}}}$Because of the magnitude difference between M_(U) and M_(L), the upperlayer decoder 1002 disregards the M_(L) component of the s′_(UL)(t).

After subtracting the upper layer from s_(UL)(t) in the subtractor 1012,the following remains:

${s_{L}(t)} = {M_{L}\mspace{14mu}\exp\left\{ {{{j\left( \;{\omega_{L} - ~\omega_{U}} \right)}t} + \theta_{L} - \theta_{U}} \right\}{\sum\limits_{m = {- \infty}}^{\infty}{S_{Lm}{p\left( {t - {mT} + {\Delta\; T_{m}}} \right)}}}}$

Any distortion effects, such as TWTA nonlinearity effects are estimatedfor signal subtraction. In a typical embodiment of the presentinvention, the upper and lower layer frequencies are substantiallyequal. Significant improvements in system efficiency can be obtained byusing a frequency offset between layers.

Using the present invention, two-layered backward compatible modulationwith QPSK doubles a current 6/7 rate capacity by adding a TWTAapproximately 6.2 dB above an existing TWTA power. New QPSK signals maybe transmitted from a separate transmitter, for example, from adifferent satellite. In addition, there is no need for linear travelingwave tube amplifiers (TWTAs) as with 16 QAM. Also, no phase errorpenalty is imposed on higher order modulations such as 8 PSK and 16 QAM.

Backward Compatible Applications

FIG. 1A depicts the relative power levels 1100 of example embodiments ofthe present invention. FIG. 11A is not to scale. This embodiment doublesthe pre-existing rate 6/7 capacity by using a TWTA 6.2 dB above apre-existing TWTA equivalent isotropic radiated power (EIRP) and secondTWTA 2 dB below the pre-existing TWTA power. This embodiment uses upperand lower QPSK layers which are non-coherent. A code rate of 6/7 is alsoused for both layers. In this embodiment, the signal of the legacy QPSKsignal 1102 is used to generate the upper layer 1104 and a new QPSKlayer is the lower layer 1110. The CNR of the legacy QPSK signal 1102 isapproximately 7 dB. In the present invention, the legacy QPSK signal1102 is boosted in power by approximately 6.2 dB bringing the new powerlevel to approximately 13.2 dB as the upper layer 1104. The noise floor1106 of the upper layer is approximately 6.2 dB. The new lower QPSKlayer 1110 has a CNR of approximately 5 dB. The total signal and noiseof the lower layer is kept at or below the tolerable noise floor 1106 ofthe upper layer. The power boosted upper layer 1104 of the presentinvention is also very robust, making it resistant to rain fade. Itshould be noted that the invention may be extended to multiple layerswith mixed modulations, coding and code rates.

In an alternate embodiment of this backwards compatible application, acode rate of 2/3 may be used for both the upper and lower layers 1104,1110. In this case, the CNR of the legacy QPSK signal 1102 (with a coderate of 2/3) is approximately 5.8 dB. The legacy signal 1102 is boostedby approximately 5.3 dB to approximately 11.1 dB (4.1 dB above thelegacy QPSK signal 1102 with a code rate of 2/3) to form the upper QPSKlayer 1104. The new lower QPSK layer 1110 has a CNR of approximately 3.8dB. The total signal and noise of the lower layer 1110 is kept at orbelow approximately 5.3 dB, the tolerable noise floor 1106 of the upperQPSK layer. In this case, overall capacity is improved by 1.55 and theeffective rate for legacy IRDs will be 7/9 of that before implementingthe layered modulation.

In a further embodiment of a backwards compatible application of thepresent invention, the code rates between the upper and lower layers1104, 1110 may be mixed. For example, the legacy QPSK signal 1102 may beboosted by approximately 5.3 dB to approximately 12.3 dB with the coderate unchanged at 6/7 to create the upper QPSK layer 1104. The new lowerQPSK layer 1110 may use a code rate of 2/3 with a CNR of approximately3.8 dB. In this case, the total capacity relative to the legacy signal1102 is approximately 1.78. In addition, the legacy IRDs will suffer norate decrease.

Non-Backward Compatible Applications

As previously discussed the present invention may also be used in“non-backward compatible” applications. In a first exemplary embodiment,two QPSK layers 1104, 1110 are used each at a code rate of 2/3. Theupper QPSK layer 1104 has a CNR of approximately 4.1 dB above its noisefloor 1106 and the lower QPSK layer 1110 also has a CNR of approximately4.1 dB. The total code and noise level of the lower QPSK layer 1110 isapproximately 5.5 dB. The total CNR for the upper QPSK signal 1104 isapproximately 9.4 dB, merely 2.4 dB above the legacy QPSK signal rate6/7. The capacity is approximately 1.74 compared to the legacy rate 6/7.

FIG. 11B depicts the relative power levels of an alternate embodimentwherein both the upper and lower layers 1104, 1110 are below the legacysignal level 1102. The two QPSK layers 1104, 1110 use a code rate of1/2. In this case, the upper QPSK layer 1104 is approximately 2.0 dBabove its noise floor 1106 of approximately 4.1 dB. The lower QPSK layerhas a CNR of approximately 2.0 dB and a total code and noise level at orbelow 4.1 dB. The capacity of this embodiment is approximately 1.31compared to the legacy rate 6/7.

“Unblind” Equalization

The performance of the IRD 500 can be improved by use of equalizers.Equalizers can be classified into two groups: those that either know orestimate the channel impulse response, and those that operate withoutsuch knowledge. Such equalizers can be found in the paper “AdaptiveEqualizer” by Qureshi, Proceedings of IEEE, Vol. 73, No. 9, September1985, and in the textbook “Digital Communications,” by John G. Proakis,Third Edition, McGraw-Hill Book Company, 1995, in Chapters 10 and 11.

The first group includes equalizers that have apriori knowledge of thechannel impulse response, and those that estimate the channel impulseresponse using prearranged training sequences known to both thetransmitter and the receiver. The second group includes blind equalizers(which have no knowledge of the channel impulse response and do notattempt to estimate it). One type of blind equalizer is a decisionfeedback blind equalizer, which uses the digital output of the system tofeedback to the equalizer computation. However, that type ofdecision-making process is very sensitive to the digital output errorrate.

The “unblind” equalizer described below does not fall neatly into any ofthe above categories. Unlike the first category, no apriori knowledge ofthe transmission channel characteristics is required, and prearrangedtraining sequences are not required, thus saving valuable transmissioncapacity. The “unblind” equalizer has the same implementation advantagesas a blind equalizer, and provides performance similar to that However,the unblind equalizer does not require specific knowledge of the channelimpulse response, nor does it need to dedicate transmission capacity totransmit training sequences. The unblind equalizer uses past receiveddata to recover the transmission signal and then uses the recoveredtransmission signal to define the equalizer format and parameters.

The unblind equalizer can also be used in combination with an adaptiveequalizer to create and adaptive unblind equalizer that can be used inapplications where the channel characteristics change over time.

FIGS. 12A and 12B are diagrams illustrating the application of unblindequalization techniques with a conventional single-layered signal. FIGS.12A and 12B will be discussed with reference to FIG. 13, which presentsan exemplary implementation of an unblind equalizer system.

Turning first to FIG. 12A, an input signal having input data ismodulated to produce modulated input signal, as shown in block 1202. Thesignal is also typically encoded with an FEC encoder such as a turboencoder. This can be accomplished, for example, by the modulator/encoder1302. The modulated signal s(t) is transmitted via channel 1304,producing signal y(t) as shown in block 1204. The signal y(t) isequalized by equalizer 1306, producing an equalized input signal ŝ(t).The equalized input signal ŝ(t) is demodulated (and decoded if wasencoded) to produce a data output, as described in block 1206. This canbe performed, for example, by the demodulator/decoder 1308 shown in FIG.13. The data output is remodulated to produce a pseudo-training sequencethat includes an idealized input signal, as shown in block 1208. Thiscan be accomplished by the remodulator 1310. Since there is a time delayassociated with this process, the resulting remodulated signal (andpseudo training sequence) is represented as s(t−τ). Next, equalizerparameters are defined from the pseudo-random training sequence, asshown in block 1210. This can accomplished in the parametergeneration/update module 1314. Next, as shown in block 1212, the inputsignal y(t) is equalized using the generated parameters. This can beperformed by the equalizer 1306 shown in FIG. 13.

In one embodiment, the equalizer parameters are generated by comparing abuffered or delayed version of the input signal with the pseudo-timingsequence. This technique is illustrated in blocks 1214 and 1216 of FIG.12B.

FIG. 14 is a diagram illustrating the embodiment shown in FIG. 13, as itcan be applied to a layered modulation system as is illustrated in FIGS.10A and 10B. Blocks 1402 and 1404 illustrate the modulation andtransmission of the upper layer signal s_(up)(t) and the lower layersignal s_(low)(t), respectively, through channel 1304 to produce signaly(t) (which is equal to S_(up)(t)+S_(low)(t). Signal y(t) is applied toa first equalizer 1306A to produce an equalized upper layer signal S_(up)(t−τ). The equalized upper layer signal S _(up)(t−τ) is applied toan upper layer demodulator 1004 and an upper layer decoder 1002 toproduce the upper layer signal. The upper layer signal is recoded byrecoder 1408, and remodulated by modulator 1006 to produce apseudo-training sequence S _(up)(t−τ). The pseudo-training sequence S_(up)(t−τ) is an idealized version of the upper layer signal, delayed byprocessing delays inherent in the recoding and remodulating process. Thesignal S _(up)(t−τ) is provided to a signal canceller or differencer1012.

Signal y(t) is delayed by a time period τ approximating that of theremodulation and recoding process by buffer 1312 to produce y(t−τ). Thisdelayed signal y(t−τ) is applied to both the parameter generation/updatemodule 1314 and a second equalizer 1306B. The equalized y(t) signal,Ŝ_(up)(t)+Ŝ_(low)(t), is provided to the differencer as well. Hence, theoutput of the differencer is S _(up)(t−τ)−[Ŝ_(up)(t−τ)+Ŝ_(low)(t−τ)].After accounting for channel transmission non-linearities, S _(up)(t−τ)is approximately equal to Ŝ_(up)(t−τ), thus, the output of the signalcanceller 1012 can be represented as a delayed and equalized version ofthe lower layer signal, or Ŝ_(low)(t−τ). This signal is provided to thelower layer demodulator 1010 and the lower layer encoder 1008 toreconstruct the lower layer signal. The parameters of the upper layerequalizer 1306A and the lower layer equalizer 1306B are updated withequalizer parameters generated or updated in the parametergeneration/update module 1314 using the buffered input signal y(t−τ) orS_(up)(t−τ)+S_(low)(t−τ) and the pseudo training sequence S _(up)(t−τ).

To an extent, the foregoing technique assumes that the transmissionchannel is wide-sense stationary or at least has characteristics thatvary slowly over time, at least as compared to the digital detectionprocess of the receiver 500. The effectiveness of the foregoingtechnique is reduced in situations where channel variances over time arenot smaller than those of the equalizer parameter update. The foregoingtechnique also assumes that even without equalization, the receiver candetect the transmitted digital information or a portion thereof at acertain range of data error rate. This may not be the case when this“unblind” equalization technique is combined for use with traditionaltraining sequence equalizers or blind equalizers.

FIGS. 15A and 15B are diagrams depicting further detail regarding thegeneration of a pseudo-training sequence. The process includes areceiving process 1520 and a remodulation process 1522. The receivingprocess 1520 is shared with the ordinary data receiving process, and isperformed by a filter 1501, timing recovery loop (TRL) module 1502, acarrier recovery loop (CRL) module 1504, and a demodulator 1004 and adecoder 1002. The decoder 1002 includes an inner decoder 1506, asynchronization bit detector module 1508 and an outer decoder 1510. Theoutput of the receiving process is a received data output. The receiveddata output is provided to an encoder or recoder 1524, which includes anouter encoder 1512, synchronization module 1514 for placingsynchronization bits in the data stream, and an inner encoder 1516. Theresulting signal is modulated by remodulator 1006, and may optionally befiltered by front end filter to produce the training sequence.

A determination may be made as to whether the unblinding pseudo trainingsequence is usable to create an equalizer parameter update. For example,at any point in the system shown in FIG. 15A, a bit error rate (BER) ofthese intermediary processes may be determined and compared to thereceived data output. For example, by using Bose, Chaudhuri, andHocquenghem (BCH) and Reed-Solomon (RS) codes, the error rate can beestimated by means of the syndrome calculation during the process. Forall other block coding, it is possible to encode the decoded vector andthereby estimate the error rate. For convolutional decoding, the errorrate may be estimated by computing the moving average of the metriccalculation. In addition to the availability of channel decoding toestimate the error rate, some communication systems have synchronizationbits in place to align the received data. With such systems, one candirectly use the synchronization bit error rate to estimate the entiredata transmission rate.

When the received data rate reaches a certain performance level, anunblinding pseudo-training sequence can be used to process the parameterupdate computation. The point at which there is sufficient channelperformance (as measured, for example, by the BER) to generate apseudo-training sequence varies from system to system, and will dependlargely on the value of other communication system parameters.

FIG. 15B is a diagram illustrating an embodiment in which the generationof the pseudo-timing sequence from the transmitted data isforeshortened. FIG. 15B differs from FIG. 15A in that the process doesnot use a complete version of the remodulation process. The remodulationstarts with the output of the inner decoder 1506. This results in asimpler remodulation process and the time required to generate theunblinding pseudo training sequence is shortened over that of the systemillustrated in FIG. 15A. However, the bit error rate may be higher.

FIGS. 13 and 14 illustrate an unblind equalization architecture thatproduces independent measurements over time.

FIG. 16 is a block diagram illustrating an unblind equalizer thatrecursively updates equalizer parameters. Comparing this embodiment withthe embodiment illustrated in FIGS. 13 and 14, the parametergeneration/update module 1604 forces its two inputs to be identicalthrough a filtering process.

FIG. 17 is a block diagram illustrating the unblind equalizer of FIG. 16as applied to a layered modulation system. This embodiment uses a singleequalizer 1602, unlike the embodiment shown in FIG. 14.

Unblind equalizers can be used in a conventional and/or an adaptivemanner. Conventionally, it is assumed that the channel 1304characteristics are either time-invariant or slowly changing in time. Insuch circumstances, once the equalizer is defined, the same equalizerparameters (e.g. structure and coefficients) can be used without furtherchange. Where the channel 1304 characteristics change significantly overtime, an adaptive unblind equalizer can be utilized. In such cases, theparameter generation/update module 1314, 1604 can continually acceptrenewed data and continue to update the parameters of the equalizer(s).

In the case of multi-layer modulation, it can generally be assumed thatthe system is capable of detecting the transmitted information withincertain error rates, even without equalization. In most cases, the upperlayer may be demodulated with a relatively low BER. However, in generalcases where the system includes only one layer of modulation, it may bedifficult to adequately detect the transmitted information withoutequalization. In such cases, the more traditional equalizers (usingtraining sequences or blind equalizers) can be used to improve thesignal, with the unblind equalizer accepting the equalized signal andproviding further performance improvements.

For example, the unblind equalizer can be used with a training sequenceequalizer. A system using a training system equalizer assumes the signalchannel is static during the data transmission. If the channel varies,the system has to wait until the next training sequence before thesystem can make any correction. The training sequence must have a lengthlong enough to be able to adequately train the equalizer, and thetraining sequence must be repeated on a periodic or a periodic basis tokeep the equalizer updated.

Although the training sequence provides perfect knowledge of thetransmitted data sequence, it consumes some of the transmittingcapacity. Hence, it is not cost effective to use a long trainingsequence, or to use a training sequence frequently.

The unblind equalizer can be used to ameliorate the weaknesses of thetraining sequence equalizer. This can be accomplished by using theunblind equalizer to update the training equalizer after the trainingsequence equalizer has established the equalizer and the communicationslink. An unblind equalizer can also be used without the need of anyadditional training sequence, once the receiver is able to receive thetransmitted data.

FIG. 18A is a diagram illustrating a state transition diagram for theuse of an unblind equalizer in combination with a training sequenceequalizer. At the beginning of the transmission, the system used thetraining sequence equalizer 1802. When the system begins receiving thetransmitted data, the system switches to select use of an unblindequalizer 1804. When a training sequence is received again, the trainingsequence equalizer 1802 is used once again, and when the trainingsequence has been received, the unblind equalizer 1804 is used again.This system takes advantage of the training sequence's perfectly matchesdata, can reduce the repeated frequency of the training sequencetransmissions (using the pseudo training sequence), and can keep theequalizer updated in a dynamically changing channel environment.

A system without a training sequence may need to have an equalizer to asufficiently error-free signal to allow the unblind equalizer tofunction effectively. In this situation, a blind equalizer can be usedbefore the unblind equalizer is employed. With the help of the blindequalizer, the system is able to receive the transmitted data. As soonas the system is able to do so, a pseudo-training sequence can bederived and the unblind equalizer can be employed. Since the unblindequalizer uses the received data as its training sequence, equalizerparameters can be more accurately determined, improving equalizerperformance.

FIG. 18B is a diagram illustrating a state transition diagram for theuse of an unblind equalizer with a blind equalizer. At the beginning ofthe transmission, the system uses a blind equalizer 1806. When thesystem begins receiving the transmitted data, the system switches toselect the use of an unblind equalizer. This technique can be used whenthe channel changes slowly compared to the data processing(demodulation, decoding, re-encoding and remodulation) time delay. Thissystem does not require any training sequence and thus improvestransmission capacity, while improving accuracy to that of the trainingsequence equalizer, and may be used in a dynamically changingtransmission channel environment.

Hardware Environment

FIG. 19 illustrates an exemplary computer system 1900 that could be usedto implement selected modules or functions of the present invention. Thecomputer 1902 comprises a processor 1904 and a memory, such as randomaccess memory (RAM) 1906. The computer 1902 is operatively coupled to adisplay 1922, which presents images such as windows to the user on agraphical user interface 1918B. The computer 1902 may be coupled toother devices, such as a keyboard 1914, a mouse device 1916, a printer,etc. Of course, those skilled in the art will recognize that anycombination of the above components, or any number of differentcomponents, peripherals, and other devices, may be used with thecomputer 1902.

Generally, the computer 1902 operates under control of an operatingsystem 1908 stored in the memory 1906, and interfaces with the user toaccept inputs and commands and to present results through a graphicaluser interface (GUI) module 1918A. Although the GUI module 1918A isdepicted as a separate module, the instructions performing the GUIfunctions can be resident or distributed in the operating system 1908,the computer program 1910, or implemented with special purpose memoryand processors. The computer 1902 also implements a compiler 1912 whichallows an application program 1910 written in a programming languagesuch as COBOL, C++, FORTRAN, or other language to be translated intoprocessor 1904 readable code. After completion, the application 1910accesses and manipulates data stored in the memory 1906 of the computer1902 using the relationships and logic that was generated using thecompiler 1912. The computer 1902 also optionally comprises an externalcommunication device such as a modem, satellite link, Ethernet card, orother device for communicating with other computers.

In one embodiment, instructions implementing the operating system 1908,the computer program 1910, and the compiler 1912 are tangibly embodiedin a computer-readable medium, e.g., data storage device 1920, whichcould include one or more fixed or removable data storage devices, suchas a zip drive, floppy disc drive 1924, hard drive, CD-ROM drive, tapedrive, etc. Further, the operating system 1908 and the computer program1910 are comprised of instructions which, when read and executed by thecomputer 1902, causes the computer 1902 to perform the steps necessaryto implement and/or use the present invention. Computer program 1910and/or operating instructions may also be tangibly embodied in memory1906 and/or data communications devices 1930, thereby making a computerprogram product or article of manufacture according to the invention. Assuch, the terms “article of manufacture,” “program storage device” and“computer program product” as used herein are intended to encompass acomputer program accessible from any computer readable device or media.

Those skilled in the art will recognize many modifications may be madeto this configuration without departing from the scope of the presentinvention. For example, those skilled in the art will recognize that anycombination of the above components, or any number of differentcomponents, peripherals, and other devices, may be used with the presentinvention.

CONCLUSION

This concludes the description of the preferred embodiments of thepresent invention. The foregoing description of the preferred embodimentof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. For example, itis noted that the uplink configurations depicted and described in theforegoing disclosure can be implemented by one or more hardware modules,one or more software modules defining instructions performed by aprocessor, or a combination of both.

It is intended that the scope of the invention be limited not by thisdetailed description, but rather by the claims appended hereto. Theabove specification, examples and data provide a complete description ofthe manufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention resides in the claimshereinafter appended.

1. A method of equalizing digital data signals, comprising the steps of:demodulating and decoding an input signal having input data to produce adata output; remodulating the data output to produce a pseudo-trainingsequence including an idealized input signal; generating equalizerparameters from the pseudo-training sequence; and equalizing the inputsignal according to the equalizer parameters.
 2. The method of claim 1,wherein the step of generating equalizer parameters from thepseudo-training sequence comprises the steps of: buffering the inputsignal; and comparing the buffered input signal to the pseudo-trainingsequence to produce the equalizer parameters.
 3. The method of claim 2,wherein the step of demodulating and decoding an input signal havinginput data to produce a data output comprises the steps of: recoveringthe carrier and timing of the input signal to produce a carrier andtiming recovered signal; demodulating the carrier and timing recoveredsignal to produce a demodulated signal; and decoding the demodulatedsignal to produce the data output.
 4. The method of claim 3, wherein thestep of remodulating the data output to produce a pseudo-trainingsequence comprises the steps of: re-encoding the data output to producea re-encoded signal; and remodulating the re-encoded signal to producethe pseudo-training sequence.
 5. The method of claim 4, wherein: thestep of decoding the demodulated signal to produce the data outputcomprises the steps of: inner decoding the demodulated signal; detectingsynchronization bits in the inner decoded demodulated signal; and outerdecoding the demodulated signal using the synchronization bits; the stepof re-encoding the data output to produce a re-encoded signal comprisesthe steps of: outer encoding the data output to produce an outer encodedsignal; and placing synchronization bits in the outer encoded signal;and inner encoding the outer encoded signal.
 6. The method of claim 3,wherein: the step of decoding the demodulated signal to produce the dataoutput comprises the steps of: inner decoding the demodulated signal;detecting synchronization bits in the inner decoded demodulated signal;and outer decoding the demodulated signal using the synchronization bitsto generate the data output; the step of remodulating the data output toproduce a pseudo-training sequence comprises the steps of: innerencoding the inner decoded demodulated signal to produce a re-encodedsignal; and remodulating the re-encoded signal.
 7. The method of claim1, wherein the input signal is equalized before being demodulated anddecoded.
 8. The method of claim 7, wherein the step of generatingequalizer parameters from the pseudo-training sequence comprises thesteps of: buffering the equalized input signal; and comparing thebuffered equalized input signal to the pseudo-training sequence toproduce the equalizer parameters.
 9. An apparatus for equalizing digitaldata signals, comprising: means for demodulating and decoding an inputsignal having input data to produce a data output; means forremodulating the data output to produce a pseudo-training sequenceincluding an idealized input signal; means for generating equalizerparameters from the pseudo-training sequence; and means for equalizingthe input signal according to the equalizer parameters.
 10. Theapparatus of claim 9, wherein the means for generating equalizerparameters from the pseudo-training sequence comprises: means forbuffering the input signal; and means for comparing the buffered inputsignal to the pseudo-training sequence to produce the equalizerparameters.
 11. The apparatus of claim 10, wherein the means foremodulating and decoding an input signal having input data to produce adata output comprises: means for recovering the carrier and timing ofthe input signal to produce a carrier and timing recovered signal; meansfor demodulating the carrier and timing recovered signal to produce ademodulated signal; and means for decoding the demodulated signal toproduce the data output.
 12. The apparatus of claim 11, wherein themeans for remodulating the data output to produce a pseudo-trainingsequence comprises: means for re-encoding the data output to produce are-encoded signal; and means for remodulating the re-encoded signal toproduce the pseudo-training sequence.
 13. The apparatus of claim 12,wherein: the means for decoding the demodulated signal to produce thedata output comprises: means for inner decoding the demodulated signal;means for detecting synchronization bits in the inner decodeddemodulated signal; and means for outer decoding the demodulated signalusing the synchronization bits; the means for re-encoding the dataoutput to produce a re-encoded signal comprises: means for outerencoding the data output to produce an outer encoded signal; means forplacing synchronization bits in the outer encoded signal; and means forinner encoding the outer encoded signal.
 14. The apparatus of claim 11,wherein: the means for decoding the demodulated signal to produce thedata output signal comprises: means for inner decoding the demodulatedsignal; means for detecting synchronization bits in the inner decodeddemodulated signal; and means for outer decoding the demodulated signalusing the synchronization bits to generate the data output; the meansfor remodulating the data output to produce a pseudo-training sequencecomprises: means for inner encoding the inner decoded demodulated signalto produce a re-encoded signal; and means for remodulating there-encoded signal.
 15. The apparatus of claim 9, wherein the inputsignal is equalized before being demodulated and decoded.
 16. Theapparatus of claim 15, wherein the means for generating equalizerparameters from the pseudo-training sequence comprises: means forbuffering the equalized input signal; and means for comparing thebuffered equalized input signal to the pseudo-training sequence toproduce the equalizer parameters.
 17. An apparatus for equalizingdigital data signals, comprising: a demodulator for demodulating aninput signal to produce a data output; a modulate; communicativelycoupled to the demodulator, for remodulating the data output to producea pseudo-training sequence including an idealized input signal; and aparameter generation module, communicatively coupled to the modulatorfor generating equalizer parameters from the pseudo-training sequence;and an equalizer, communicatively coupled to the parameter generationmodule, for equalizing the input signal according to the equalizerparameters.
 18. The apparatus of claim 17, wherein the input signal iscoded, and the apparatus further comprises: a decoder, coupled betweenthe demodulator and the modulator, for decoding the demodulated inputsignal to produce the data output; and a coder, coupled between themodulator and the decoder, for encoding the remodulated data output toproduce the pseudo-training sequence.
 19. The apparatus of claim 17,wherein the equalizer is communicatively coupled to the input signal andthe demodulator, and wherein the apparatus further comprises: a buffer,coupled between the input signal and the parameter generation module,for buffering the input signal.
 20. The apparatus of claim 19, whereinthe parameter generation module compares the buffered input signal tothe pseudo-training sequence to produce the equalizer parameters. 21.The apparatus of claim 17, wherein the equalizer is communicativelycoupled to the input signal and the apparatus further comprises: abuffer, communicatively coupled between the equalizer and the parametergeneration module, for buffering the equalized input signal.
 22. Theapparatus of claim 21, wherein the parameter generation module comparesthe buffered input signal to the pseudo-training sequence to produce theequalize parameters.
 23. The apparatus of claim 17, further comprising:a timing recovery and carrier recovery module communicatively coupledbetween the input signal and the demodulator; an inner decodercommunicatively coupled to the demodulator; a synchronization bitdetector, communicatively coupled to the inner decoder; an outerdecoder, communicatively coupled to the synchronization bit detector,the outer decoder producing a received data output based on the inputsignal; an outer encoder, communicatively coupled to the outer decoder,the outer encoder producing an outer encoded signal; a synchronizationmodule, communicatively coupled to the outer encoder, thesynchronization module for placing synchronization bits in the outerencoded signal; an inner encoder, communicatively coupled between thesynchronization module and the modulator.
 24. The apparatus of claim 17,further comprising: a timing recovery and carrier recovery modulecommunicatively coupled between the input signal and the demodulator; aninner decoder communicatively coupled to the demodulator; asynchronization bit detector, communicatively coupled to the decoder; anouter decoder, communicatively coupled to the synchronization bitdetector, the outer decoder producing a received data output based onthe input signal; and an inner encoder communicatively coupled betweenthe inner decoder and the modulator.